1. Field of the Invention
This disclosure relates to a light emitting device and a manufacturing method thereof.
2. Discussion of the Related Art
An organic light emitting device among flat panel display devices is a self luminescent display device that emits light by electrically exciting an organic compound. Because an LCD using an organic light emitting device does not require a backlight, a decrease in weight and thickness of the LCD is possible and manufacturing processes can be simplified. Further, the organic light emitting device can be manufactured in a low temperature, has a high response speed of 1 ms or less, and has characteristics such as low power consumption, a wide viewing angle, and a high contrast.
The organic light emitting device comprises an organic emitting layer between an anode and a cathode. The organic light emitting device forms an exciton, which is a hole-electron pair, by coupling a hole received from the anode and an electron received from the cathode within the organic light emitting layer and emits light by generating energy when the exciton returns to a ground level.
The organic light emitting device is divided into a top emission type and a bottom emission type depending on the emission direction of light generated from the organic emitting layer. In a case where an organic light emitting device, comprising a pixel driving circuit, is a bottom emission type, the aperture ratio is seriously limited because the pixel driving circuit occupies a wide area of the substrate. Accordingly, in order to improve the aperture ratio, a top emission type organic light emitting device was introduced.
FIG. 1 is a cross-sectional view of a light emitting device in the related art. Referring to FIG. 1, a buffer layer 105 is positioned on the substrate 100 and a gate electrode 110 is positioned on the buffer layer 105. The first insulating layer 115, which is a gate insulating layer, is positioned on the gate electrode 110. An amorphous silicon layer 120 is positioned on the first insulating layer 115 so that a predetermined area thereof may correspond to the gate electrode 110.
Ohmic layers 125a and 125b, defining a source area and a drain area, are positioned on the predetermined area of the amorphous silicon layer 120. The ohmic layers 125a and 125b may comprise amorphous silicon in which impurity ions are injected.
The source electrode and the drain electrode 130a and 130b are positioned on the ohmic layers 125a and 125b. The second insulating layer 140, comprising a via hole 145 for exposing a portion of the drain electrode 130b, is positioned on the substrate comprising the source electrode and the drain electrode 130a and 130b. 
The first electrode 150, electrically connected to the drain electrode 130b through the via hole 145, is positioned on the second insulating layer 140. The first electrode 150 may be an anode or a cathode. When the first electrode 150 is an anode, the first electrode 150 may comprise a transparent conductive layer such as Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), Indium Cerium Oxide (ICO), or Zinc Oxide (ZnO). When the first electrode 150 is a cathode, the first electrode 150 may comprise magnesium (Mg), silver (Ag), aluminum (Al), calcium (Ca), or alloys thereof.
A fourth insulating layer 160, comprising an opening 165 for exposing a portion of the first electrode 150, is positioned on the substrate comprising the first electrode 150. An organic emitting layer 170 is positioned within the opening 165 and a second electrode 180 is positioned on the substrate comprising the organic emitting layer 170.
At least six mask processes are required to manufacture an organic light emitting device having the above structure. That is, a gate electrode, an amorphous silicon layer and ohmic layer, a source electrode and drain electrode, a via hole, a first electrode, and an opening are formed by stacking layers made of a predetermined material and then etching the layers using a mask.
The number of masks required for a process increases manufacturing costs increases and the process time is lengthened.